TOO CLOSE FOR COMFORT: Charles Nagle -- who is being detained in connection with stalking "Law & Order" star Kathryn Erbe -- appears in a snapshot he arranged with the actress on set last year. Photo: Redthink Media

“Law & Order: Criminal Intent” star Kathryn Erbe reluctantly posed for a picture with her lovesick stalker after he dragged his young daughter to the show’s Bronx set and accosted her during a break, The Post has learned.

Charles Nagle had already spent two years penning disturbing love letters to Erbe, the popular actress who plays an NYPD Major Case squad detective, when he made the unwanted appearance last year.

The honey-blond performer, who plays a cop hellbent on getting into the minds of criminals, became terrified when Nagle introduced himself — realizing immediately the Philadelphia man asking for a picture was her creepy superfan, sources said.

Disgusted and clearly anxious, Erbe somehow managed to keep her cool and play the part of accommodating star — flashing half a smile for the camera with the repulsive fan by her side, the sources said.

It was the first time the slick-black-haired Nagle — a self-described romantic songwriter and crooner who goes by the stage name “Chaz Rose” — caught up with the actress known for playing Detective Alexandra Eames for nearly the past decade.

Erbe, a mother of two who lives in Brooklyn, alerted NBC and the show’s security to be on guard about Nagle as a possible problem. But for Nagle, who is married with two young daughters, the photo became his money shot.

He soon cropped his daughter out of the photo — leaving behind an image of him with his arm around Erbe’s shoulder — and used it as his Facebook image.

On MySpace, Nagle maintained a blog entry devoted solely to Erbe and her show where he chatted about how much he adored her.

A source told The Post, which broke the story Monday, that Nagle sent Erbe “letters of adulation for years about how much he loved her . . . He was totally obsessed.” The source called it “a case of unrequited love.”

Nagle, 36, showed up at a second film shoot a few months ago and tried to talk her once again.

Erbe was again calm and collected in keeping Nagle’s affection at arm’s length, but she finally went to the real NYPD detectives after the lovelorn loser learned the names and addresses of her closest relatives and began sending amorous missives about her to them.

NYPD detectives, armed with an arrest warrant, picked up Nagle last week in Philadelphia. He’s being held there awaiting an extradition hearing slated for next Wednesday, said a spokesman for the Philadelphia District Attorney’s Office.